Unit 4: Nervous System Flashcards
Central nervous system
Processing and control center of the nervous system
Stores sensory information, creates thoughts, emotions and memories
Consists of the brain and spinal cord.
Brain
Control center of nervous system
In cranial cavity
Divided into the brainstem, cerebellum, diencephalon, and cerebrum
Spinal cord
Continuous with the medulla oblongata and descends into vertebral canal
Consists of 31 segments with 31 pairs of spinal nerves
Peripheral nervous system
Consists of cranial and spinal nerves and the special sense organs
Sensory and motor functions
Sensory receptors
Somatic nervous system, autonomic nervous system, enteric nervous system
Sensory receptors
- detect changes in the internal and external environment
- located throughout the body
- relays information via afferent nerve fibers to the CNS
- signals from CNS are sent via efferent (motor) nerve fibers to trigger motor responses in glands and muscle tissue.
Somatic nervous system
Voluntary nervous system
Somatic sensory (afferent) nerve fibers transmit sensory info from receptors to CNS
Somatic motor (efferent) fibers relay impulses from CNS to skeletal system
Autonomic nervous system
Involuntary nervous system
Autonomic sensory (afferent) fibers that transmit info from receptors (visceral organs) to the CNS.
Autonomic motor (efferent) fibers relay impulses from CNS to smooth muscle, cardiac muscle and glands
- sympathic division
- parasympathetic division
Sympathetic
Stimulatory role
Parasympathetic
Inhibitory role
Enteric nervous system
Enteric plexus of nerves extending throughout the GI tract
Involuntary
Peristalsis
Glandular secretion
Peristalsis
waves of smooth muscle contraction, propelling food through GI tract
Neurons
Sensory neurons
Interneurons
Motor neurons
Sensory neurons
transmit stimuli from body to CNS
Interneurons
remain within CNS, process and store information
Motor neurons
Transmit stimuli from CNS to the body
Classifications of neurons
Unipolar
Bipolar
Multipolar
Unipolar neurons
dendrites and a single axon extending as a a fused process from cell body (usually located in ganglia)
dendrites extend individually from cell body and function as sensory receptors
Bipolar
Have one dendrite and one axon extending from cell body
Part of special sensory organs: retina of the eye, inner ear, and olfactory bulb
Multipolar
Typically have multiple dendrites and a single axon extending from cell body
Make up majority of the CNS
Neuroglia of CNS
Astrocytes, oligodendrocytes, microglial cells, ependymal cells
Astrocytes
largest and most abundant neuroglia
multiple cytoplasmic processes that extend from star-shaped cell bodies
provides connection with capillaries, neurons, synaptic endings, and pia mater
protoplasmic astrocytes
Astrocytes Function
Anchorage to neurons
blood-brain barrier–protects from harmful substances
take up and recycle excess ions and neurotransmitters
Passage for exchange of nutrients between capillaries and neurons
secrete chemicals that guide migration and growth of neuron
repair damaged tissue
Protoplasmic astrocytes
Distinguished by short, branching cytoplasmic processes reside in mater
Fibrous astrocytes
longer, unbranched cytoplasmic processes reside in white matter
Oligodendricytes
smaller than astrocytes, with few cytoplasmic processes
wrap tightly around the axons of neurons in the CNS, covering them with layer of myelin sheath for insulation
forms segments of sheath around several axons at once
Microglial cells
smallest of neuroglia in the CNS
long, thorn-like cytoplasmic processes extedning from small ovoid cell bodies
Ependymal cells
single rows of cuboidal to columnar epithelial cells, lining ventricles of the brain and central canal of spinal cord
secrete and monitor CSF
form semi-permeable barrier between csf and the interstitial fluid of the cns
have microvilli and cilia at their apical surface which help circulate csf
Neuroglia of PNS
Schwann cells and satellite cells
Schwann cells
function similarly to oligodendrocytes
form myelin sheaths around the axon of the neurons
function in regeneration of neurons of the PNS by guiding and stimulating regrowth
Many are needed to myelinate a single axon
unmyelinated gaps are known as Nodes of Ranvier
Satellite cells
flat cells surrounding neuronal cell bodies residing within ganglia
provide structural support and form a barrier, regulating the exchange of substances
Myelination
covering made of lipid and protein that surrounds axons neurons
insulates neurons and speeds up neuronal impulses
increase in amount with age
Nerve
cord-like structure composed of bundles of neuronal axons that transfers sensory information to the CNS and/or motor information from the CNS
Structures of the nervous tissue
Different anatomical features of a nerve
Action potentials
Ion channels, leakage channel, ligand-gated channel, mechanically gated channel, voltage-gated channel, membrane potential, Na+/K+ pump, depolarization, hyperpolarization
Ion channels
flow down electrochemical gradient, from high concentration to low
flow of charged ions creates electrical charge called current
Leakage channel
open and close randomly and independent of stimuli
plasma membrane more K+ than Na+ channels
Ligand-gated channel
open in response to binding of ligands (neurotransmitters/hormones)
Mechanically gated channel
open due to mechanical forces– vibrations, touch, pressure, etc.
i.e. auditory receptors in the ears, touch receptors on skin
Voltage-gated channel
open due to change in membrane potential – voltage
Membrane Potential
- build up of negative charged ions in the cytosol inside the membrane
- build up of positive charged ions in the extracellular fluid outside membrane
Na+/K+ Pump
- Na+ higher in extracellular fluid
- K+ higher in cytosol
- Actively pumps 3 Na+ ions out of the cell, 2 K+ ions move into the cell (keep cytosol
more negative)
Depolarization
- Plasma membrane becomes less negatively charged (-70 mV to -40 mV)
- must hit threshold potential for action potential to be triggered
- “all or nothing”
Hyperpolarization
- Cytoplasm becomes more negatively charged than resting membrane potential
- Membrane decreases to about -90 mV due to slow closure of potassium gates
Refractory period
- Absolute: no possibility of another stimulus (inactivated Na+ channels)
- Relative: sodium channels open but only very strong stimulus can cause action
potential (K+ still open making depolarization harder)
Continuous conduction
- Unmyelinated axons
- Sodium influx creates a local region of positive charge on inside of axon compared to
outside - Creates difference between axon depolarized and adjacent region at resting potential
- Creates flow of current, propagates as a wave toward axon terminal
Saltatory conduction
- Myelinated axons
- Myelinated sections lack voltage-gated channels – no action potential there
- Action potential jumps from node to node
What affects speed of propagation?
Myelination and speed
What is the specific stimulus of the different receptors?
- Mechanoreceptor: mechanical force (touch, pressure, vibration, stretch)
- Thermoreceptor: temperature
- Photoreceptor: light
- Chemoreceptor: chemicals
- Nociceptor: chemical released at tissue damage
- Osmoreceptor: osmotic pressure
What is contained in the brainstem?
Diencephalon
Thalamus. Hypothalamus, and epithalamus
Functions of the diencephalon
Cerebrum cortex
frontal lobe, temporal lobe, parietal lobe, occipital lobe
Frontal lobe
cognitive thought and memory, and control of voluntary movements
Temporal lobe
primary auditory area (hearing)
wernicke’s area (speech comprehension)
Parietal lobe
body orientation, primary gustatory cortex (taste)
Occipital lobe
primary visual cortex, visual interpretation
Cerebrum hemispheres
folds (gyri) and creases (sulci)
Cerebrum: Meninges
- Pia mater: innermost layer
- Subarachnoid space: CSF circulation
- Arachnoid mater: spider web-like appearance
- Dura mater: outermost layer
- Meningeal layer: dural folds
- Sinuses: peristeal and meningeal layers separate to create dural sinuses
- Sigmoid: main site of drainage
Importance of blood-brain barrier?
Spinal Nerves
- Cervical Plexus
- Brachial Plexus: arm nerves (axillary, radial, ulnar, median, musculocutaneous)
- Lumbar Plexus: leg nerves (femoral – largest, obturator, iliohypogastric,
ilioinguinal, genitofemoral, lateral femoral cutaneous) - Sacral and Coccygeal Plexus
What are the different reflexes?
Sympathetic vs parasympathetic nervous systems
